Stator core and motor device including the same

ABSTRACT

Disclosed is a stator core including a core back fixedly inserted onto an outer surface of a stationary member, a plurality of teeth protruding from the core back in an outer diameter direction, wherein a coil is wound around the plurality of teeth so as to allow magnetic flux from a magnet to flow to the teeth, front end portions defining outer edges of the teeth, respectively, and body portions defining a length of the teeth and having a width increasing from the core back toward the front end portions, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2010-0070514 filed on Jul. 21, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stator core and a motor deviceincluding the same, and more particularly, a stator core having animproved stator core shape to maximize current characteristics and motorefficiency, and a motor device including the same.

2. Description of the Related Art

Electric motors are devices that convert electrical energy intomechanical energy, and may be classified into various kinds according totypes of power being supplied thereto, driving methods, rotor types andexterior structures associated with frames, brackets and the like.Furthermore, the electric motors, classified as above, may bere-classified according to insulating methods, bearing types, outputs,number of rotations, voltage, frequency and the like.

Among those motors, a spindle motor installed inside an Optical DiskDrive (ODD) rotates a disc so that an optical pickup unit moving in alinear direction can read data recorded on the disc.

Disk drives are applicable to portable multimedia devices such as laptopcomputers that are handy to carry and use anywhere and anytime. Therehas been a demand for thinner disk drives to cope with a current trendtoward smaller portable media devices.

Most spindle motors, currently being installed in disk drives, have astator core produced by the following processes: stacking a plurality ofcore sheets, pressed silicon steel plates, forming an insulating layeron the resultant stack and winding a coil therearound. In this case, anelectromagnetic force, generated by current flowing in the wound coil,acts as the cause of rotational torque of spindle motors.

However, as a motor is driven according to the related art, eddy currentis increasingly generated, causing defective motor operation, and BackElectro Motive Force (Back-EMF) waveforms are rendered sharp, degradingthe efficiency of the motor.

Moreover, the stator core provided as a stack of cores interruptsmagnetic flux from a magnet to the cores, due to the stacked structurethereof. This may accelerate magnetic saturation in the ends of thecores, thereby degrading motor efficiency.

Therefore, an optimized design for a stator core is being currentlydemanded in order to minimize the loss of a motor while ensuring motorcharacteristics.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a stator core, capable ofminimizing the loss of a motor by rendering magnetic flux, flowing froma magnet to a core, smooth and capable of enhancing the characteristicsof a motor by reducing eddy current loss, and a motor device includingthe same.

According to an aspect of the present invention, there is provided astator core including: a core back fixedly inserted onto an outersurface of a stationary member; a plurality of teeth protruding from thecore back in an outer diameter direction, wherein a coil is wound aroundthe plurality of teeth so as to allow magnetic flux from a magnet toflow to the teeth; front end portions defining outer edges of the teeth,respectively; and body portions defining a length of the teeth andhaving a width increasing from the core back toward the front endportions, respectively.

The body portions may respectively include indented portions, each beingdepressed in one surface of a corresponding one of the body portionswhile protruding to the other surface thereof.

The indented portions may have circumferential surfaces with the samediameter.

Each of the indented portions may be formed in an outer portion of acorresponding one of the body portions.

The teeth may be formed to satisfy a conditional expression below:

$0.57 \leq \frac{( {{Wmax} - {\Phi \; D}} )}{Wmin} < 1.4$

where Wmin denotes a width of each of the body portions to which thecore back is connected, ΦD denotes a diameter of a circumferentialsurfaces of each of the indented portions, and Wmax denotes a width ofeach of the body portions in which the centers of the indented portionsare placed, respectively.

The teeth may be formed to satisfy a conditional expression below:

$0.85 \leq \frac{B}{A} \leq 0.95$

where B denotes a radius of a circumference drawn along respectivecenters of the indented portions while being centered on the center ofthe core back, and A denotes a radius of a circumference drawn alongrespective outer surfaces of the front end portions while being centeredon the center of the core back.

According to another aspect of the present invention, there is provideda motor device including: a stationary member having an insertion holetherein; a rotating member inserted in the insertion hole to berotatable relative to the stationary member; and a stator core includinga core back fixedly inserted onto an outer surface of a stationarymember, a plurality of teeth protruding from the core back in an outerdiameter direction, wherein a coil is wound around the plurality ofteeth so as to allow magnetic flux from a magnet to flow to the teeth,front end portions defining outer edges of the teeth, respectively, andbody portions defining a length of the teeth and having a widthincreasing from the core back toward the front end portions,respectively.

The body portions may respectively include indented portions havingcircumferential surfaces with the same diameter, the indented portionseach being depressed in one surface of a corresponding one of the bodyportions while protruding to the other surface thereof.

The teeth may be formed to satisfy a conditional expression below:

$0.57 \leq \frac{( {{Wmax} - {\Phi \; D}} )}{Wmin} < 1.4$

where Wmin denotes a width of each of the body portions to which thecore back is connected, ΦD denotes a diameter of a circumferentialsurfaces of each of the indented portions, and Wmax denotes a width ofeach of the body portions in which the centers of the indented portionsare placed, respectively.

The teeth may be formed to satisfy a conditional expression below:

$0.85 \leq \frac{B}{A} \leq 0.95$

where B denotes a radius of a circumference drawn along respectivecenters of the indented portions while being centered on the center ofthe core back, and A denotes a radius of a circumference drawn alongrespective outer surfaces of the front end portions while being centeredon the center of the core back.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-sectional view illustrating a motor deviceincluding a stator core according to an exemplary embodiment of thepresent invention;

FIG. 2 is a schematic perspective view illustrating a stator coreaccording to an exemplary embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view taken along line A-A of FIG.2, illustrating a stator core according to an exemplary embodiment ofthe present invention;

FIG. 4 is a schematic perspective view illustrating a single core sheetof a stator core according to an exemplary embodiment of the presentinvention;

FIG. 5 is a schematic cross-sectional view taken along line B-B of FIG.4, illustrating a single core sheet of a stator core according to anexemplary embodiment of the present invention;

FIG. 6 is a schematic plan view illustrating lines of magnetic forcearound an indented portion of a stator core according to an exemplaryembodiment of the present invention;

FIG. 7 is a schematic plan view illustrating a stator core according toan exemplary embodiment of the present invention; and

FIG. 8 is a graph illustrating the waveforms of Back-EMF of a motordevice including a stator core according to an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. The invention may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

In the drawings, the same reference numerals will be used throughout todesignate the same or like components having the same function.

FIG. 1 is a schematic cross-sectional view illustrating a motor deviceincluding a stator core according to an exemplary embodiment of thepresent invention.

Referring to FIG. 1, a motor device 500 including a stator core 110,according to an exemplary embodiment of the present invention, mayinclude a stator 100 including a stator core 110, a rotor 200, a bearingassembly 300, and a disk chucking device 400.

Concrete embodiments of the stator core 110 will be described later. Themotor device 500 according to the present invention may possess all ofthe features associated with each of the embodiments of the stator core110.

The stator 100 may refer to a stationary member with an insertion holetherein, that is, every stationary part other than rotating parts.However, for the ease of description, the stator 100 is described andillustrated as including the stator core 110 and a winding coil 120.

The stator 100 is a stationary part that includes the winding coil 120and the stator core 110. The winding coil 120 generates anelectromagnetic force having a predetermined magnitude when power isapplied thereto. The stator core 110 is formed by stacking a pluralityof core sheets 110 a about which the winding coil 120 is wound.

The winding coil 120 is electrically connected with a flexible printedcircuit board such that external power is supplied thereto.

In this case, the stator 100 is fixed by a base 320 to be describedlater, and the winding coil 120 of the stator 100 is placed so as toface a magnet 220 attached to the inner surface of a rotor case 210.

The rotor 200 refers to a rotatable member rotating relative to thestationary member, and is inserted into the insertion hole of thestationary member so as to be rotatable therein.

The rotor 200 includes the rotor case 210 shaped like a cup. The rotorcase 210 has the magnet 220 having a ring shape along the innercircumferential surface thereof. Here, the magnet 220 is a permanentmagnet having magnetic north and south poles alternately magnetized in acircumferential direction to thereby generate a magnetic force having apredetermined magnitude.

The rotor case 210 includes a rotor hub 212 and a magnet support portion214. The rotor hub 212 is fixedly inserted onto the shaft 310, and themagnet support portion 214 has the ring-shaped magnet 220 disposed alongthe inner surface thereof.

The rotor 200 is rotated by an electromagnetic interaction between thering-shaped magnet 220 and the winding coil 120 wound about the statorcore 110. Namely, as the rotor case 210 of the rotor 200 is rotated, theshaft 310 interworking with the rotor case 210 is rotated.

The bearing assembly 300 may include a base 320, the shaft 310, a sleeve330, and a thrust plate 340.

The base 320 may be assembled by fixedly inserting the sleeve 330 into areceiving hole of the base 320.

The sleeve 330 may have a shaft hole to bind the shaft 310 therein. Aplurality of radial dynamic pressure grooves may be formed in the innersurface of the shaft hole.

The shaft 310 is rotatably inserted into the shaft hole of the sleeve330, and may be elongated in the direction of the axis of rotation.

Here, the thrust plate 340 is formed on the lower surface of the shaft310 to thereby reduce a frictional force relative to the shaft 140during rotation.

Furthermore, one end portion of the shaft 310 coming into contact withthe thrust plate 340 may be formed to have a predetermined radius ofcurvature.

A ring-shaped stopper 350 is provided on the upper portion of the thrustplate 340. Corresponding with the ring-shaped stopper 350, a portion ofthe outer circumferential surface of the shaft 310 may be depressedtoward the axis of the shaft 310 to thereby form a ring-shaped catchingrecess.

The inner circumferential surface of the stopper 350 is inserted intothe catching recess to thereby prevent the shaft 310 from escapingupwardly out of the sleeve 330.

The thrust plate 340 overlies a support plate 360. The support plate 360is engaged with the base 320 and serves to support the shaft 310.

The disk chucking device 400 may include a centering case 410, achucking member 420 and an elastic member 430. The inner circumferentialsurface of a disc D may be secured to the center case 410.

When the disc D is press-fitted thereto, the elastic member 430 iscompressed by the chucking member 420, so that the compression elasticforce and restoring force of the elastic member 430 securely fixes thedisc D to the center case 410.

FIG. 2 is a schematic perspective view illustrating the stator coreaccording to an exemplary embodiment of the present invention. FIG. 3 isa schematic cross-sectional view taken along line A-A of FIG. 2,illustrating the stator core according to an exemplary embodiment of thepresent invention. FIG. 4 is a schematic perspective view illustrating asingle core sheet of the stator core according to an exemplaryembodiment of the present invention. FIG. 5 is a schematiccross-sectional view taken along line B-B of FIG. 4, illustrating thesingle core sheet of the stator core according to an exemplaryembodiment of the present invention.

Referring to FIGS. 2 through 5, the stator core 110 according to anexemplary embodiment of the present invention may be formed by stackingcore sheets 110 a.

The core sheets 110 a are prepared by pressing silicon steel plates. Thestator core 110 may be formed as the plurality of core sheets 110 a arestacked on top of one another.

Furthermore, the core sheet 110 a may have respective indented portions115 that are necessarily provided due to the addition of the stackingprocess. The indented portions 115 are coupled with one another tothereby ensure the stable stacking of the core sheets 110 a for thestator core 110.

Here, the stator core 110 may include a core back 112 and teeth 118.

The core back 112 may have an opening to be fixedly inserted onto thestationary member. That is, the core back 112 may be fixedly insertedonto the base 320 of the stationary member. The opening may be placedin, for example, the center of the core back 112.

Furthermore, the core back 112 may have an annular shape. However, theshape of the core back 112 and the location of the opening are notlimited to the drawing or description, and may be modified in variousmanners.

That is, the core back 112 may be modified to have various shapes, suchas a quadrangular frame shape, a hexagonal frame shape, an octagonalframe shape and the like, so as to conform with the shape of the outercircumferential portion of the base 320.

Terms regarding directions are defined as follows: an outer diameterdirection refers to a direction towards the outer circumferentialsurface of the ring-shaped core back 112 on the basis of the innercircumferential surface thereof, an inner diameter direction refers to adirection toward the inner circumferential surface of the core back 112on the basis of the outer diameter direction thereof. That is, the outerdiameter direction refers to a direction toward the outer edges of theteeth 118 from the base 320, the stationary member, while the innerdiameter direction refers to a direction toward the base 320 from theouter edges of the teeth 118.

The teeth 118 protrude from the core back 112 in the outer diameterdirection. The winding coil 120 is wound around the teeth 118, so thatmagnetic flux from the magnet 200 can flow thereto.

The teeth 118 may each include a front end portion 116 defining theouter edge of a corresponding one of the teeth 118 in the outer diameterdirection, and a body portion 114 defining the length of thecorresponding one.

Here, the respective front end portions 116 of the teeth 118 may haveouter surfaces rounded such that the stator core 110 has an overallcircular shape.

Each of the body portions 114 may have a gradually increasing width fromthe core back 112 toward the front end portion 112 thereof. Thiscontributes to reducing eddy current loss while improving currentproperties to thereby optimize the performance of the motor device 500including the stator core 110.

Furthermore, each of the body portions 114 may have the indented portion115 functioning when the core sheets 110 a are stacked in order to formthe stator core 110. The indented portion 115 may be depressed in onesurface of the body portion 114 while protruding to the other surfacethereof.

The indented portions 115, necessarily provided due to the addition ofthe process of stacking the core sheets 110 a, may have circumferentialsurfaces with the same diameter and be formed in the outer portions ofthe body portions 114, respectively.

The structure of the indented portion 115 and the disposition thereof onthe body portion 114 will now be described with reference to FIGS. 6through 8.

FIG. 6 is a schematic plan view illustrating lines of magnetic forcearound the indented portion of the stator core according to an exemplaryembodiment of the present invention. FIG. 7 is a schematic plan viewillustrating the stator core according to an exemplary embodiment of thepresent invention. FIG. 8 is a graph illustrating the waveforms ofBack-EMF of the motor device including the stator core according to anexemplary embodiment of the present invention.

Referring to FIGS. 6 and 7, the teeth 118 of the stator core 110,according to this exemplary embodiment, protrude from the core back 112in the outer diameter direction. Also, the winding coil 120 is woundaround the teeth 118 to thereby allow magnetic flux from the magnet 220to flow thereto.

As for the stator core 110, the core sheets 110 a are made to be thinenough to render the magnetic flux smooth, and these thinned core sheets110 a are stacked to thereby form the stator core 110. This contributesto minimizing eddy current loss and thus optimizing current and motorefficiency.

In this case, the indented portion 115 is formed in each of the bodyportions 114 in order to prevent the undesired separation between thecore sheets 110 a being stacked. However, these indented portions 115may interrupt the magnetic flux flowing from the magnet 220 into thestator core 110.

That is, as shown in FIG. 6, the magnetic flux around the indentedportion 115 of the body portion 114 is interrupted by the diameter ‘ΦD’of the indented portion 115, undesirably accelerating magneticsaturation ‘S’ at the end portion of the stator core 110 and thusdegrading the performance and efficiency of a motor.

For the purpose of drastically reducing the magnetic saturation causedby the indented portion 115, as shown in FIG. 6, the width Wmin of thebody portion 114 to which the core back 112 is connected, the diameterΦD of the circumferential surface of the indented portion 115, and thewidth Wmax of the body portion 114 in which the center of the indentedportion 115 is placed, satisfy the following conditional expression 1:

$\begin{matrix}{0.57 \leq \frac{( {{Wmax} - {\Phi \; D}} )}{Wmin} < 1.4} & ( {{Conditional}\mspace{14mu} {expression}\mspace{14mu} 1} )\end{matrix}$

The following table 1 shows the result of experiments upon Back-EMF bythe indented portion 115, the flatness of the stator core 110, andnoise.

TABLE 1 Coil (Wmax − Magnetizing Winding Number BACK-EMF Core Noise ΦD)/voltage (V) outer of Vrms Vpp flatness [dB] Wmin @1200 μF diameter Turns@1500 rpm @1500 rpm 70 um↓ @1.4 KHz 0.57 600 0.23 mm 32 620 1.71 52 430.60 600 0.23 mm 32 642 1.78 48 39 0.80 600 0.23 mm 32 649 1.81 48 361.00 600 0.23 mm 32 657 1.83 42 42 1.20 600 0.23 mm 32 660 1.83 46 441.40 600 0.23 mm 32 659 1.83 86 56 1.60 600 0.23 mm 32 661 1.80 102 67

As it is seen from Table 1 above, a reduction in the level of noise, aswell as core flatness, is achieved when 0.57≦(Wmax−ΦD)/Wmin<1.4.

Meanwhile, the stator core 110 may be implemented to satisfy thefollowing conditional expression 2, together with or independently ofthe above conditional expression 1.

$\begin{matrix}{0.85 \leq \frac{B}{A} < 0.95} & ( {{Conditional}\mspace{14mu} {expression}\mspace{14mu} 2} )\end{matrix}$

where B denotes the radius of a circumference drawn along the respectivecenters of the indented portions 115 while being centered on the centerof the core back 112, and A denotes the radius of a circumference drawnalong the respective outer surfaces of the front end portions 116 whilebeing centered on the center of the core back 112.

When B/A is greater than 0.95, the indented portion 115 is placedexcessively adjacent to the front end portion 116. This may help inpreventing the separation of the core sheets 110 a being stacked;however, this makes it difficult to control the flatness after thestacking and brings about limitations in using a manufacturing mold.Therefore, the stator core 110 may be formed within the range ofconditional expression 2 above.

Furthermore, referring to FIG. 8, it can be seen that the waveform ofthe Back-EMF of the motor device 500 including the stator core 110according to this exemplary embodiment is a sine wave having a bellshape.

Accordingly, the stator core 110, according the exemplary embodiments ofthe present invention, is provided with the body portions 114 having agradually increasing width and the indented portions 115 satisfying theabove conditional expressions 1 and 2, thereby achieving a reduction ineddy current loss and thus enhancing the characteristics of the motordevice 500.

Furthermore, since the magnetic flux from the magnet 220 to the core isrendered smooth, the performance of a motor is not deteriorated.

As set forth above, in the stator core and the motor device includingthe same according to exemplary embodiments of the invention, magneticflux flowing to the core from the magnet is rendered smooth, therebypreventing the deterioration of a motor's performance.

Furthermore, motor characteristics can be enhanced by reducing eddycurrent loss and thus causing the Back-EMF waveform to have a sinecurve.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1-10. (canceled)
 11. A stator core comprising: a core back fixedlyinserted onto an outer surface of a stationary member; a plurality ofteeth protruding from the core back in an outer diameter direction,wherein a coil is wound around the plurality of teeth so as to allowmagnetic flux from a magnet to flow to the teeth; front end portionsdefining outer edges of the teeth, respectively; and body portionsdefining a length of the teeth, each body portion including an indentedportion positioned in an outer portion of a corresponding one of thebody portions, and each indented portion positioned closer to acorresponding front end portion than the core back.
 12. The stator coreof claim 11, wherein: the body portions each having a width increasingfrom the core back toward the front end portions, respectively, and eachindented portion being depressed in one surface of a corresponding oneof the body portions while protruding to the other surface thereof. 13.The stator core of claim 12, wherein the indented portions havecircumferential surfaces with the same diameter.
 14. The stator core ofclaim 11, wherein the teeth are formed to satisfy a conditionalexpression below:$0.57 \leq \frac{( {{Wmax} - {\Phi \; D}} )}{Wmin} < 1.4$where Wmin denotes a width of each of the body portions to which thecore back is connected, ΦD denotes a diameter of a circumferentialsurfaces of each of the indented portions, and Wmax denotes a width ofeach of the body portions in which the centers of the indented portionsare placed, respectively.
 15. The stator core of claim 11, wherein theteeth are formed to satisfy a conditional expression below:$0.85 \leq \frac{B}{A} < 0.95$ where B denotes a radius of acircumference drawn along respective centers of the indented portionswhile being centered on the center of the core back, and A denotes aradius of a circumference drawn along respective outer surfaces of thefront end portions while being centered on the center of the core back.16. A motor device comprising: a stationary member having an insertionhole therein; a rotating member inserted in the insertion hole to berotatable relative to the stationary member; and a stator corecomprising: a core back fixedly inserted onto an outer surface of astationary member; a plurality of teeth protruding from the core back inan outer diameter direction, wherein a coil is wound around theplurality of teeth so as to allow magnetic flux from a magnet to flow tothe teeth; front end portions defining outer edges of the teeth,respectively; and body portions defining a length of the teeth, eachbody portion including an indented portion positioned in an outerportion of a corresponding one of the body portions, and each indentedportion positioned closer to a corresponding front end portion than thecore back.
 17. The motor device of claim 16, wherein: the body portionseach having a width increasing from the core back toward the front endportions, respectively, and each indented portion having circumferentialsurfaces with the same diameter, the indented portions each beingdepressed in one surface of a corresponding one of the body portionswhile protruding to the other surface thereof.
 18. The motor device ofclaim 16, wherein the teeth are formed to satisfy a conditionalexpression below:$0.57 \leq \frac{( {{Wmax} - {\Phi \; D}} )}{Wmin} < 1.4$where Wmin denotes a width of each of the body portions to which thecore back is connected, ΦD denotes a diameter of a circumferentialsurfaces of each of the indented portions, and Wmax denotes a width ofeach of the body portions in which the centers of the indented portionsare placed, respectively.
 19. The motor device of claim 16, wherein theteeth are formed to satisfy a conditional expression below:$0.85 \leq \frac{B}{A} < 0.95$ where B denotes a radius of acircumference drawn along respective centers of the indented portionswhile being centered on the center of the core back, and A denotes aradius of a circumference drawn along respective outer surfaces of thefront end portions while being centered on the center of the core back.